Internally switched multiple range transducers

ABSTRACT

Systems and methods for an internally switched multiple range transducer are provided. In one embodiment, a method comprises receiving, at a first sensor, a pressure, wherein the first sensor is associated with a first pressure range; measuring, at the first sensor, the pressure to generate a first pressure signal; in response to determining that the first pressure signal is not associated with the first pressure range, activating a second sensor, wherein the second sensor is associated with a second pressure range that is different from the first pressure range; and measuring, at the second sensor, the pressure to generate a second pressure signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation claiming priority under 35 U.S.C.§120 to U.S. patent application Ser. No. 13/196,035, filed Aug. 2, 2011,which is a continuation of U.S. patent application Ser. No. 12/384,821,filed Apr. 9, 2009, now U.S. Pat. No. 7,997,143, issued on Aug. 16,2011, all of which are entitled “INTERNALLY SWITCHED MULTIPLE RANGETRANSDUCER,” and all of which are hereby incorporated by reference intheir entirety as if fully set forth herein.

FIELD OF THE INVENTION

This invention relates to pressure transducers and more particularly toan array of multiple pressure transducers wherein a selected one isswitched into operation according to the pressure range being monitored.

BACKGROUND OF THE INVENTION

As one can ascertain it is often necessary to measure pressure with ahigh degree of accuracy and across a relatively large pressure range.Typical accuracy is specified as a percent of full scale. Therefore,even when a pressure transducer is manufactured with an extreme accuracytolerance it may prove to be relatively inaccurate at the lower portionof the pressure range. Also it is often of interest to resolveaccurately a relatively small differential pressure coupled to a fairlyhigh line pressure. In both cases it is desirable that multiple sensingelements or multiple transducers, each of which is optimized for aspecific portion of the pressure range, be employed. In the prior art,multiple pressures are measured employing multiple pressure transducers.For example, see U.S. Pat. No. 6,401,541, entitled “MULTIPLE PRESSURESENSING SYSTEM,” issued on Jun. 11, 2002 to Anthony D. Kurtz, aninventor herein, and assigned to Kulite Semiconductor Products, Inc. Inthat patent there is shown a plurality of pressure transducers whereeach can measure a different pressure range and are coupled to a singleremote processor. In that particular patent it is a desire to measuremultiple pressures by using multiple pressure transducers, but whichtransducers are exposed to different environments and where the pressurefrom each transducer is measured during a different interval. In anyevent, as one can ascertain from the above noted patent, there is shownmultiple pressure transducers, switching devices and a microcontrollerwhich controls the switching devices, and selects given sequences toaccess said transducers. The above noted patent is hereby incorporatedin its entirety.

The present invention uses multiple sensing elements and an appropriateswitching device to condition the signal, the internal functionality ofthe transducer would provide a continuous output proportional to theapplied pressure over a large pressure range but with significantlyenhanced accuracy. It is also understood that the assignee, Kulite, hasmany patents regarding the design and operation of pressure transducersin all types of environments and in all types of ranges. The presentinvention thus employs multiple pressure transducers which areselectively switched into operation or selectively utilized according toa different pressure range. Thus, according to the present invention,one would employ multiple sensing elements each of which is optimizedfor a specific portion of the pressure range and each of which isselected according to that portion of the pressure range being measured.

SUMMARY OF THE INVENTION

A plurality of pressure sensors, each responsive to an associatedpressure range, wherein each sensor can accommodate a different pressurerange to enable accurate pressure measurements over a wide range equalto the sum of said different ranges, means coupled to said plurality ofpressure sensors and operative to select any one of said sensorsaccording to the magnitude of an applied pressure, said selected sensordetermined by whether said applied pressure is within the desiredoperating range of said sensor.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of an internally switched multiple rangetransducer, according to this invention

FIG. 2 is a block diagram of an alternate embodiment of such atransducer.

FIG. 3 is a block diagram of another embodiment of such a transducer.

FIG. 4 is a schematic representation of a sensor arranged as aWheatstone bridge configuration.

FIG. 5 is a top-plan view of an integrated circuit which can be employedtogether with this invention.

FIG. 6 is a schematic block diagram of another embodiment of ainternally switched multiple range transducer according to thisinvention.

DETAILED DESCRIPTION OF THE FIGURES

Referring to FIG. 1, there is shown a block diagram of a switchedmultiple range transducer according to this invention. As ascertainedabove pressure transducers are designed to operate over various pressureranges. As also indicated, it would be desirable to measure pressurewith a high degree of accuracy, across a relatively large pressurerange. Thus, when a transducer is manufactured with an extreme accuracytolerance it may prove relatively inaccurate at the lower portion of thepressure range. In FIG. 1, there are depicted pressure sensors ortransducers 10, 20 and 30. While the number of pressure transducersshown is three, it is indicated that the system can accommodate more. Inany event, a pressure range is specified between 0 psi through N psi. Asseen, the first pressure transducer designated P.sub.1 10 operates overa range of 0 to X psi. This is a low pressure range and, for example,may be a range of zero (0) to fifteen (15) psi, while the secondpressure transducer is designed to be accurate over a range of X to Ypsi, where X is fifteen (15) psi and Y may be, for example, one hundred(100) psi or greater. The third pressure transducer, 30, will operateover a range from Y psi to N psi, which for example may be two hundred(200) or three hundred (300) psi and so on.

In order to explain the invention it is shown that the total pressurerange is therefore broken up into three (3) ranges, whereby pressuretransducer 10 operates to accommodate range one (1), as indicated bymodule 26, pressure transducer 20 is designed to operate over the rangeof X to Y or range two (2), as designated by module 27, while pressuretransducer 30 is designated to operate over the range of Y to N asdesignated by module 28. Module 25, designated as a range selector andcontrol module also receives a pressure, and for example, may be asingle pressure transducer which produces a voltage output across theentire range. The voltage output from the coarse pressure transducer inrange selector 25, determines the range for the applied P. In thismanner, the range selector determining the range selects a module as 11,21 and 31. One of the transducers 10, 20 or 30 operates in that range asdetermined by module 25. Therefore, if the value of pressure is greaterthan X than the range selector and controller 25 would select pressuretransducer 20 and pressure transducer 20 would be switched via selector21 to the processing combiner 15 and hence to the output amplifier 16where a voltage would be provided at the output, indicative of thevoltage output of pressure transducer 20. It is also seen, that one canhave an analog output voltage via module 16, or one can take the outputof amplifier 16 and convert it to a digital signal via the analog todigital converter 17 to produce a digital output. As one can ascertainfrom FIG. 1, the range selector and control device 25 determines whatrange the pressure P is in, and then selects a suitable sensor ortransducer 10, 20 or 30 for operation in this range.

The pressure sensor, for example, that can be selected as pressuresensor 10 via selector 11, pressure sensor 20 via selector 21 orpressure sensor 30 via selector 31. The selectors can be switches orother devices. The switches can be semiconductor switches and so on.Basically, as one can ascertain from FIG. 1, the multiple pressuresensors as 10, 20 and 30 are each optimized for a specific portion ofthe pressure range that they operate in. The multiple sensing elementsare selected via selectors 11, 21 and 31 which may be switches ascontrolled by the range selector 25. Thus, the system produces an outputover the entire pressure range as from 0 to N psi via output amplifier16. This produces a reliable and consistent output for a user, wherebyeach of the separate pressure transducer operates efficiently within agiven range and, therefore, selection of one of the transducers for therange produces a continuous high-accurate output.

It is understood that in regard to pressure transducers, one normallyemploys a diaphragm which can be fabricated from silicon or some othersemiconductor or other material. The natural frequency of a diaphragm isimportant as it is the frequency which the diaphragm is most sensitiveor resonates at. It is known that the greater the thickness of thediaphragm the higher the natural frequency, while the greater the areathe lower the natural frequency. The natural frequency is inverselyproportional to the square of the radius of a diaphragm. Since siliconhas a very high stiffness to density ratio, with a modulus essentiallyequal to that of steel and a density comparable to aluminum, togetherwith the fact that high piezoresistive coefficients of siliconpiezoresistors and small size have resulted in transducers with highnatural resonant frequencies. In any event, it is known that foraccurate low frequency measurements a pressure transducer should employa relatively large diaphragm which can be of a given thickness.Therefore, pressure transducer 10 would be differently manufactured thanpressure transducer 20 or pressure transducer 30.

As will be explained further, a pressure transducer normally is aWheatstone bridge configuration where each of the bridge resistors arepiezoresistive devices. A semiconductor bridge is secured to a siliconor other diaphragm to fabricate a pressure or force transducer such astransducers 10, 20 and 30. Also as indicated above because of theoperating range the transducers are different, as for example eachtransducer 10, 20 and 30 may have a different active area or may beseparate transducers having different diaphragm thicknesses as well asdifferent active areas. As seen from FIG. 1, the range selector andcontrol 25 receives pressure P and contains a pressure sensor whichoperates over an entire range. Depending on the voltage output of therange selector pressure transducer in module 25, the range selector bydetermining the voltage output, selects one of the transducers 10, 20 or30 according to the desired range and the selection is done by selectors11, 21 and 31 which, as indicated above, can be switches. These switchescan be semiconductor switches or mechanical switches or any other typeof switch. Thus, as seen in FIG. 1, a major aspect of the presentinvention is to provide multiple sensing elements, or multipletransducers, each of which is optimized for a specific portion of thepressure range to be employed.

Referring to FIG. 2, there is shown an alternate embodiment of aswitched multiple range transducer. As seen in FIG. 2, there is no rangeselector and control module as 25. There are again, three pressuretransducers as shown by example as transducer 40, 41 and 42. Eachtransducer, as before, is designed to operate over a selected range. Forexample, pressure transducer 40 operates over the range of zero (0) to Xpsi while pressure transducer 41 operates over the range of X to Y psi,and transducer 42 operates over the range of Y to Z psi. In any event,it is also shown that pressure transducer, as for example 41 may operateover the range of X.sup.1 to Y. X.sup.1 could be slightly greater thanX, or slightly smaller than X, to enable one to build in a pressuredelay in regard to operating these switches.

The system of FIG. 2 operates as follows. Each pressure transducer as40, 41 and 42 is associated with a switch module, as pressure transducer40 is associated with switch 46, pressure transducer 41 is associatedwith switch 47 and pressure transducer 42 is associated with switch 48.Each of the switches is associated with a separate reference level, asreference level 43 for switch 46, reference level 44 for switch 47 andreference level 45 for switch 48. First, assume that the pressure is inthe range of 0 to X psi. In this range the switch 50 is closed and theoutput of pressure transducer 40 is applied to an input of a summingamplifier 55. Switch 46 will operate when the voltage from P.sub.1exceeds a predetermined reference level value. When switch P.sub.1operates contact 50 opens and contact 51 and contact 52 closes. Thesecontacts are operated by the switch and are shown in schematic form. Inany event, switch 47 operates contact 52 so the output of pressuretransducer 41, indicative of the range X to Y psi is now provided to aninput of the summing amplifier 55. If the pressure rises then switch 47operates. When switch 47 (P2) operates as controlled by reference levelgenerator 44, contact 52 again opens, while contact 54 and 53 areclosed. This now enables the output of pressure transducer 42 to beapplied via switch 48 to an input of the output amplifier 55. It is alsoseen that reference level generator 43 is coupled to reference levelgenerator 44 while reference level generator 44 is coupled to referencelevel generator 45. In this manner the reference voltages are addedtogether to produce a difference reference level for each of thereference level generators. Because the voltages are coupled via aresistor network, this enables better temperature tracking and so on.Thus, as one can easily see from FIG. 2, if the pressure starts out at ahigh value then switch 46 operates to open contact 50 and to closecontact 51 and 52 if the reference level from generator 44 is within apredetermined value, if not then switch 48 will operate contact 53 andso on. Thus it is seen that during any range depending on the voltageoutput from the pressure transducers and the reference level generatedone of the switches as 46, 47 or 48 will operate, enabling one of thepressure transducers to be coupled to output amplifier 55. Eachtransducer, as indicated, is indicative of a particular pressure range.It is also seen that the output of amplifier 55 can be coupled to ananalog digital converter 56 to produce a digital signal at the output,or can produce a signal indicative of a pressure range of zero (0) to Zpsi at the output of the amplifier 55.

Referring to FIG. 3, there is shown still an alternate embodiment of thepresent invention. FIG. 3 shows three pressure transducers as 61, 61 and62 each associated and designed to accommodate a given pressure range asindicated above. Each pressure transducer has its output coupled to ananalog digital converter as A/D converter 63 for pressure sensor 60, A/Dconverter 64 for pressure sensor 61, A/D converter 65 for pressuresensor 62. Each pressure sensor as indicated above is associated andaccurately designed for a given pressure range. The output from eachpressure transducer is converted to a digital signal by the associatedA/D converter. These digital signals are applied to a microprocessor 70at the real time inputs. The microprocessor 70 scans each digital inputand determines what the pressure range is. This is easily done, as forexample, if the pressure range is ten (10) psi the microprocessorunderstands that the input from pressure transducer P.sub.1 is the mostaccurate input and, therefore, processes this input to produce anoutput. If the microprocessor sees that the pressure exceeds, forexample, X psi, but does not exceed Y psi, then it immediately processesand connects the output from pressure transducer 61 to the output lead.If the microprocessor 70 determines that the pressure exceeds Y psi,then it couples the output from pressure sensor or transducer 62 to themicroprocessor output. The microprocessor program is a simple programand can make an easy determination. The output of microprocessor goes toa digital analog converter 66 to produce an output signal which is ananalog signal over the given voltage range of zero (0) to Z psi, asindicated. It is understood, that while three transducers are shown, onecan have more than three. It is also understood that one can havemultiple headers, or multiple pressure transducers, in an associatedheader, where each transducer is optimized for a desired portion of therange or one can utilize a single header with multiple sensors ortransducers, each optimized separately.

The fabrication of pressure transducers as indicated above is well knownand Kulite Semiconductor Products, the assignee herein, has many suchtransducers which will operate accordingly. FIG. 3 also shows atemperature unit 67, which sends a digital signal indicative of thesystem operating temperature to the microprocessor 70. Hence themicroprocessor 70 can compensate for temperature operation of eachtransducer as 60, 61 and 62. This scheme is shown in U.S. Pat. No.4,192,005, entitled “COMPENSATED PRESSURE TRANSDUCERS EMPLOYING DIGITALPROCESSING TECHNOLOGY,” issued on Mar. 4, 1980 to A. D. Kurtz andassigned to Kulite.

Referring to FIG. 4, there is shown a typical pressure sensorconfiguration. As indicated, a pressure sensor comprises a Wheatstonebridge, normally having four (4) piezoresistors as 80, 81, 82 and 83.The bridge is biased by a positive voltage and has its output taken asshown. In this manner, as a pressure is applied the piezoresistors varyin resistance to cause the bridge to produce a voltage outputproportional to the applied pressure. The applied pressure flexes thediaphragm and hence causes piezoresistors to change resistance. Thus,the sensor as seen produces a given voltage for a given appliedpressure. This voltage of course determines the applied pressure and,therefore, any monitoring circuit coupled to the Wheatstone bridge wouldknow or determine what the pressure range is by determining the voltageoutput from the bridge.

FIG. 5 depicts a top plan view of the semiconductor chip having locatedthereon three (3) diaphragms designated as 90, 91 and 92. It is shownthat each diaphragm, or the active area of each diaphragm, is different.Each of the diaphragms will have the same thickness, but differentactive areas. Thus, FIG. 5 depicts a single chip multiple range pressuretransducer devices, each of which has a silicon substrate having aplurality of simultaneously formed thin regions where the thin regionsare the diaphragm regions. Each has the same minimum thickness. Aplurality of piezoresistor circuits are formed on the silicon substratewithin the active area. Each of the thin regions deflects a differentamount upon application of a common pressure thereto. Whereby, whenexcited, each of the circuits provides an output indicative of thecommon pressure over a different operating range. This configuration isdepicted in great detail in U.S. Pat. No. 6,642,594, entitled “SINGLECHIP MULTIPLE RANGE PRESSURE TRANSDUCER DEVICE,” issued on Nov. 4, 2003to A. D. Kurtz, an inventor herein, and assigned to Kulite SemiconductorProducts, Inc., the assignee herein. That patent is incorporated in itsentirety within this application. See also U.S. Pat. No. 6,861,276issued on Mar. 1, 2005, entitled “METHODS OF FABRICATING A SINGLE CHIPMULTIPLE RANGE PRESSURE TRANSDUCER DEVICE,” by A. D. Kurtz and assignedto the assignee herein. As indicated from the above noted patents thesemiconductor wafer such as that depicted in FIG. 5 has three sensorseach located within an active area as 90, 91 and 92 where each activearea is of a different dimension, where each diaphragm has the samethickness and, therefore, each of the diaphragms and the sensorsassociated with the diaphragms will operate in different pressureranges. FIG. 5 shows three such diaphragm areas while the above notedpatent shows two such diaphragm areas. In any event, it is apparent thattwo or more diaphragm areas can be employed obtaining the benefits oftransducers which can operate over different pressure ranges.

Referring to FIG. 6, there is shown still another embodiment which canbe employed. In FIG. 6 there are shown three pressure sensors as 95, 96and 97. Each pressure sensor is associated with a switch as 110 forpressure sensor 95, 111 for pressure sensor 96 and 112 for pressuresensor 97. As seen each voltage output of the pressure sensors isdirected to the input of a comparator. Thus, pressure sensor 95 iscoupled to comparator 103, comparator 103 is also coupled to a referencelevel generator 100. In a similar manner the output of pressure sensor96 is coupled to the input of comparator 104 which compares the outputof sensor 96 with reference level generator 101. The output of pressuresensor 97 is coupled to comparator 105 which is associated with areference level generator 102. Each comparator can operate therespective switch as 110, 111 and 112. As seen in FIG. 6, switch 110 isnormally closed, thus applying bias and operating potential to thebridge 95. If the pressure level is within the range of 0 to X psi thencomparator 103 keeps switch 110 closed while switches 111 and 112 areopen. Thus, only the output from bridge 95 is directed to the outputamplifier 120. If the pressure rises, then the voltage output from thebridge 95 will increase until it exceeds the reference level 100 atwhich time comparator 103 will open switch 110 and close switch 111. Inthis manner, the pressure transducer 96 will determine the output as itis the only transducer which receives a voltage. As the pressure risesthen reference level generator 100 will cause comparator 104 to operate.When comparator 104 operates it again opens switch 111 and closes switch112, which enables the pressure sensor 97, or bridge 97, to be connectedto the input of the output amplifier 120. It is understood each of thediaphragms may have a stop which will prevent the diaphragm from furtherdeflecting once a maximum deflection is set.

As one can ascertain, the way the circuit operates is that comparator103 which is coupled to reference level generator 100 is always operatedto cause contact 110 to be open because the output of the bridge 95 willalways be at a high voltage as the pressure exceeds X psi. The diaphragmassociated with bridge 95 will not deflect as it will be stopped at agiven pressure and cannot deflect any further. In the same manner, ifthe pressure exceeds Y psi then comparator 104 continues to operate tokeep contact 112 closed and contact 111 open. If the pressure goes downand goes into the range between X to Y psi, then comparator 103 willcause switch 111 to close giving circuit control to bridge 96. Again ifthe pressure goes down so that it is in the range of 0 to X psi thenswitch 110 closes, placing sensor 95 in operation and receiving bias.This happens because comparator 103 will be in its quiescent statecausing switch 110 to close, placing sensor bridge 95 in operation. Thebridge 96 and 97 do not receive operating potential and, therefore, donot affect the output. As the pressure rises beyond X psi thencomparator 103 operates to open switch 110 and, therefore, remove biasfrom bridge 95 and close switch 111 to enable sensor bridge 96 tocontrol the output 120.

A pressure transducer and switch combination which would operate inregard to the diagram in FIG. 6 is depicted in U.S. Pat. No. 6,545,610,issued on Apr. 8, 2003 to A. D. Kurtz, et al. and assigned to KuliteSemiconductor Products, Inc., the assignee herein. That patent entitled“PRESSURE TRANSDUCER AND SWITCH COMBINATION” shows a piezoresistivebridge coupled to a comparator to produce an output when a pressureexceeds a predetermined threshold. That circuit can be used for thecomparators shown in FIG. 6. In any manner it should be clear from theabove-noted discussion that one can provide a multiple range transducerby utilizing multiple sensing elements as multiple transducers and anappropriate switching circuit which can be an analog or digital circuitto condition the signal. Thus, each of the multiple sensors ortransducers can be designed to accurately accommodate a given pressurerange and can be employed to produce an output when the applied pressureis within that range. In this manner, the most accurate and efficientsensor is used for each of the plurality of pressure ranges to bemeasured, therefore, providing a high degree of accuracy across arelatively large pressure range. It should be apparent to one skilled inthe art that there are many alternate ways of accomplishing theabove-noted invention, all of which are deemed to be encompassed withinthe spirit and claims appended hereto.

What is claimed is:
 1. A method, comprising: receiving, at a firstsensor, a pressure, wherein the first sensor is associated with a firstpressure range; measuring, at the first sensor, the pressure to generatea first pressure signal; in response to determining that the firstpressure signal is not associated with the first pressure range,activating a second sensor, wherein the second sensor is associated witha second pressure range that is different from the first pressure range;and measuring, at the second sensor, the pressure to generate a secondpressure signal.
 2. The method of claim 1, further comprising: inresponse to determining that the second pressure signal is associatedwith the second pressure range, outputting the second pressure signal.3. The method of claim 1, further comprising: in response to determiningthat the first pressure signal is not associated with the first pressurerange, deactivating the first sensor.
 4. The method of claim 1, whereinthe first pressure range and the second pressure range form a contiguouspressure range.
 5. The method of claim 1, further comprising: inresponse to determining that the second pressure signal is notassociated with the second pressure range, deactivating the secondsensor.
 6. The method of claim 1, further comprising: generating a firstreference level; and wherein determining that the first pressure signalis not associated with the first pressure range is responsive todetermining that the first pressure signal is at least a first referencelevel.
 7. The method of claim 1, further comprising: generating a firstreference level; and wherein determining that the second pressure signalis associated with the second pressure range is responsive todetermining that the second pressure signal is at least a firstreference level.
 8. The method of claim 1, further comprising:generating a first reference level and a second reference level; andwherein determining that the second pressure signal is associated withthe second pressure range is responsive to determining that the secondpressure signal is between a first reference level and a secondreference level.
 9. The method of claim 1, wherein each of the firstsensor and the second sensor is a semiconductor pressure sensor having adiaphragm.
 10. The method of claim 9, wherein a thickness of thediaphragm of each of the first sensor and the second sensor are aboutequal.
 11. The method of claim 9, wherein a cross-sectional area of thediaphragm of the first sensor is associated with the first pressurerange and a cross-sectional area of the diaphragm of the second sensoris associated with the second pressure range.
 12. A method, comprising:receiving, at a first sensor and a second sensor, a pressure, whereinthe first sensor is associated with a first pressure range and thesecond sensor is associated with a second pressure range that isdifferent from the first pressure range; measuring, at the first sensor,the pressure to generate a first pressure signal; measuring, at thesecond sensor, the pressure to generate a second pressure signal; inresponse to determining that the first pressure signal is not associatedwith the first pressure range, determining whether the second pressuresignal is associated with the second pressure range; and in response todetermining that the second pressure signal is associated with thesecond pressure range, outputting the second pressure signal.
 13. Themethod of claim 12, further comprising: generating a first referencelevel; and wherein determining that the first pressure signal is notassociated with the first pressure range is responsive to determiningthat the first pressure signal is at least a first reference level. 14.The method of claim 12, further comprising: generating a first referencelevel; and wherein determining that the second pressure signal isassociated with the second pressure range is responsive to determiningthat the second pressure signal is at least a first reference level. 15.The method of claim 12, further comprising: generating a first referencelevel and a second reference level; and wherein determining that thesecond pressure signal is associated with the second pressure range isresponsive to determining that the second pressure signal is between afirst reference level and a second reference level.
 16. The method ofclaim 12, wherein the first pressure range and the second pressure rangeform a contiguous pressure range.
 17. The method of claim 12, whereineach of the first sensor and the second sensor is a semiconductorpressure sensor having a diaphragm.
 18. The method of claim 17, whereina thickness of the diaphragm of each of the first sensor and the secondsensor are about equal.
 19. The method of claim 17, wherein across-sectional area of the diaphragm of the first sensor is associatedwith the first pressure range and a cross-sectional area of thediaphragm of the second sensor is associated with the second pressurerange.
 20. The method of claim 17, wherein each of the diaphragms of thefirst sensor and the second sensor include a piezoresistive array.